1. Field of the Invention
This invention relates to a process for manufacturing flat-type element for electrophoresis comprising a medium membrane placed between two sheets and an apparatus advantageously employable for performing the process. More particularly, this invention is to provide a process and an apparatus for manufacturing an element for electrophoresis which is easy to handle and advantageously employable for performing autoradiography.
2. Description of Prior Arts
A procedure of flat-type electrophoresis is performed based on the fact that substances in a conductive medium membrane migrate differently in the electric field depending upon the nature of the substance. Electrophoresis is regarded inevitable for separation and analysis of substances originating from living body such as protein and nucleic acid in biochemistry and medical science. Particularly, the flat-type electrophoresis is inevitable in the procedure for determination of base sequence of DNA which is frequently performed in genetic engineering or study of hereditary disease, because it is required to compare respective migration distances of four kinds of base-specifically cleaved DNA products or mixtures of base-specifically chain prolonged DNA products.
In the conventional process for flat-type electrophoresis, a polymer gel lacking in self-supporting nature such as agarose and polyacrylamide is used in the form of membrane (layer) which is prepared by forming a gel on a support or between two supports. However, the gel formed on a support is easily broken in the procedure of forming the gel on a support, a procedure of placing the gel in a device for electrophoresis, storage of the gel or a procedure of applying a sample on the gel. Further, the gel is sometimes damaged by inadvertently dropping something other than sample on the gel. Accordingly, much attention and skill are required to handle it. In a conventional process of vertical electrophoresis wherein a mold is made of two glass plates for forming a gel therebetween and the mold is kept vertical in the electrophoresis procedure, it is difficult to prepare a mold with uniform thickness and is also difficult to introduce a gel forming solution into a mold of narrow space before the solution becomes gel. Therefore, specific skill is also required. Particularly, in the procedure for determination of base sequence of DNA, it is desired to prepare a long gel medium so as to analyze DNA segments as many as possible. It is, however, difficult to prepare and to handle such a long gel medium. It is further disadvantageous that the glass plate is easily broken.
In the procedure of electrophoresis, the components to be analyzed in an analyte are labeled with radioisotope and separated through electrophoresis. Subsequently, the image of the separated components in the analyte is given by autoradiography. This process includes a procedure of placing the medium membrane for electrophoresis containing radioisotope on a radiographic film for recording the radiation emitted therefrom in layers and allowing to stand them (this procedure is called "exposure"). During this procedure, it is required, in the case that the flat type gel membrane is employed, to cover the radiographic film with a water impermeable thin sheet such as a plastic wrapping sheet to prevent the film from wetting. In the case that a gel is formed between two glass plates, it is required to replace one glass plate with a thin film (for keeping the radiation emitted from isotope in analyte in the gel from being absorbed and remarkably reduced which takes place when a radiation passes through a glass plate). In this procedure of removing the glass plate, it often happens that a gel is inadvertently broken, or a portion of the gel is sticked to the upper glass plate and the other portion of the gel is sticked to the lower glass plate. Therefore, skill is required to remove one glass plate without damaging the gel. Further, when the gel medium is covered with a thin sheet such as a plastic wrapping sheet, foams are sometimes introduced and left between the gel and sheet, or the sheet is apt to be wrinkled, thereby decreasing adhesiveness between the gel and the radiographic film. As a result, the obtained autoradiograph is apt to be unclear and the resolution nature decreases.
As a result of study by the present inventors for obviating the above defects, they have discovered that a flat-type element for electrophoresis provided with a medium membrane for electrophoresis between a support and a cover sheet having thickness of not more than 50 .mu.m is easy to handle in the procedure of electrophoresis and the subsequent exposure and recording procedures without possibility of rapturing a gel medium membrane. They have already applied the above invention for patent under the Japanese Patent Application No. 58(1983)-1324.
The above-mentioned invention has an advantage that a gel medium membrane employed as a medium for electrophoresis is easy to handle without possibility of being broken. Moreover, in the case that a self-supporting porous membrane (e.g., continuous micro-porous membrane of cellulose acetate, filter paper) is employed as a medium membrane, said invention can also gives the above advantage.